A modern programming language that makes developers happier.

kotlinlang

Hello all, I am trying to figure out the best way to include a data classes inherited fields in hashCode and equals methods.  Code in thread

```open class Foo(
   var foo: String? = null
)```
```data class Bar(
   val bar: String,
): Bookmark() {
   // implement my hashCode and equals to account for bar and foo fields.
}```
Since a data class does not include inherited fields in hashCode and equals I will need to provide my own implementation.  I did try to implement hashCode and equals in Foo, but that doesn’t help either with inheritance.  If there are a lot of fields in Bar, this leads to a lot of “boilerplate” code.  Is there a way to take advantage of Bars already implemented hashCode and equals methods?

Possibly this for equals using ‘===’?
```override fun equals(other: Any?): Boolean {
   return  (other is Bar) &amp;&amp;
           this === other &amp;&amp;
           foo == other.foo
}```

One simpler option is to override the property in your data class constructor:

```kotlin
data class Bar(
    val bar: String,
    override val foo: String? = null,
) : Foo()```

<https://pl.kotl.in/RJoah-tNj>
overriding in the constructor is the _only_ way to take advantage of the `data class` at all, really

Thank you both, makes a ton of sense and was not at all obvious to me at first thought.

How about
```data class Bar(val bar: String, val foo: Foo): Foo by foo```

It depends on the semantics of the different parts, but yes that's also a good option

btw I'm not sure you can extend a *class* by delegation like this, it would probably require to turn `Foo` into an interface first